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Joined: Dec 2004
Posts: 78
Cinner Offline OP
In the 2002 Code book, can some explain the difference between tables 16, 17 and 18. What is the difference between "service equipment" and "ac system"?

Joined: Feb 2003
Posts: 231
Service equipment is your service panel and associated items. Example your building main.

AC System is intended to mean an electrical installation in which the energy provided by that installation to utilization equipment is derived from a single energy source. For example, an electrical installation supplied from a transformer bank or a transformer is considered an AC System. An installation supplied by a different transformer would be considered a different system.

****NOTE- This all applies only to the 2002 CEC as there have been changes to this in the 2006 CEC. The changes are at the bootom.

Table 16- is used to find the size of the bond conductor.

Ex. You have a water heater that is fed from a double 30 amp breaker. According to the table the minimum size required for the Bond conductor is 12 awg.

Table 17 is used to find the minimum size of Grounding conductor for AC Systems.

Ex. Your house has a 100 amp service. The main breaker is 100 amp and your service conductors are #3 awg RW90. The table goes by the ampacity of the largest service conductor. So according to table 2 #3awg RW90 has an ampacity of 105 amps. So using Table 17 the minimum size Grounding conductor has to be #6awg.

Table 18 was used for grounding a service raceway and equipment that was fed from an ungrounded delta system. Use the table to find out what size grounding conductor is used to ground the service equipment enclosure to ground.

The changes to these Tables in the 2006 CEC are:

Table 16 has been changed to relate to the largest ungrounded conductor and not the size of the overcurrent device.

Table 17 is now called Minimum Size Of Grounding Conductor.

Table 18 has been deleted.

I hope this helps.

Joined: May 2003
Posts: 1,158

Joined: Jun 2006
Posts: 613
Table 18 exist in BC again. the 2006 code made som very big changes to Grounding and bonding conductors. For some very sound technical reasons the BC code committee did not adopt the changes to tables 17 and 18.
T17 is the minimum size of grounding conductor for AC systems or common grounding conductor. and would apply for services and secondaries of isolated distribution transformers or other seperately derived systems.
T18 is for grounding conductors for service raceway and service equipment. Bonding jumpers and ground conductor sizing for ungrounded systems.
It should also be mentioned that t16 is now based on conductor size not the overcurrent device. It can have a big impact if you say upsize conductors for voltage drop on a string of parking lot lights and forget to upsize the bonding conductor too. Alternately you will be good with the number 12 bonding conductor for a motor with a 24 amp fla fed with #10 on a 40 or 50 amp breaker. Thus making teck cable a good wiring method for a motor.

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